Skis and snowboards typically include a core, a structural layer surrounding the core, a base, and an outer layer covering the top or the top and sides of the ski. By far the most common structural layer is fiberglass impregnated with a thermosetting resin, notwithstanding that the thermoset/fiberglass layer is difficult to work with and requires substantial curing periods during the production process. Other composites using thermosetting resins are equally difficult and time-consuming to use. For example, forming an injection-molded ski with a thermoset is commonly carried out by laying the uncured preimpregnated fiberglass (or other composite) on a plastic top sheet and placing both in a heated die to form an outer shell. The die shapes the shell with heat and pressure. An average of ten minutes is required to cure the fiberglass. Once the outer shell is cured, the lower surface of the fiberglass is specially prepared for bonding by abrading, cleaning, applying a primer, or other method. The shell is then placed in a jig with a base, the base having edges and a fiberglass/thermoset resin structural layer. The foam core is then injected between the base and the top and joins the two together by bonding to the roughened fiberglass surface. The bond occurs by the foam penetrating into the roughened surface of the fiberglass and curing.
Before the outer shell and base are placed in the jig, the surfaces of the fiberglass that are to come in contact with the foam to join the top and base to the foam core must be roughened so that the mechanical bond between these parts is strong enough to avoid premature delamination between them. Significant chemical bonding does not take place between the cured fiberglass layers and the foam core. Thus, even with careful surface sanding to increase the mechanical bond strength, some degree of delamination, and thus degradation of the flex characteristics or structure of the ski, may occur over time.
The steps of laying up the wet fiberglass/thermosetting resin composite, waiting for it to cure, and preparing the surfaces to bond well with the foam are labor intensive, time consuming, and imprecise. Thus, the cost of the ski is high even though relatively low-cost materials are used.
Skis with a torsion box construction also include top layers or outer shells that must be bonded to the top and, possibly, sides of the torsion box. A torsion box is a load-beating shell that completely surrounds the core of the ski. The torsion box is constructed of a high modulus fiber sock (fiberglass, carbon, KEVLAR (trademark), or ceramic) impregnated with a thermosetting resin material. The core is typically constructed of wood, such as fir or spruce, or may be a polyethylene foam. The current wrapping and curing processes using a thermosetting resin with the fiber sock are also very time-consuming and difficult.
Skis with tops that include a top layer such as that described above, or any with an outer shell that extends not only over the top surface of the ski, but also down the sides from edge to edge have recently become very popular. However, one problem with such shells is the lack of thermal stability of the acrylic or urethane material of which they are made. These materials lack stability and rigidity to the point that many blemished skis are produced due to the shrinkage that occurs when the shell cools after being placed on the ski. As the shell cools it contracts and, from time to time, dimples, bumps, or other discontinuities occur.
Because of the above-described drawbacks of the present methods and construction of skis, the present invention was developed. Use of the method and construction of the present invention will reduce manufacturing times and errors inherent in making skis with foam-injected cores, skis with other cores, and skis with edge-to-edge outer shells.